The invention relates to an oil wiping ring for pistons of internal combustion engines, having a lamella consisting of strip steel, provided with parallel walls, whose working surface has a barrel-shaped asymmetrical shape, having a vertex line that extends over the circumference of the lamella, whereby a spreading spring disposed in a ring groove of the piston and having one spring groove wall facing away from the piston crown side and one spring groove wall facing the piston crown side presses the lamella radially against the cylinder wall.
In order to prevent too much motor oil from getting into the combustion chamber, which not only results in high oil consumption but also has negative effects on the emission behavior of the engine, a sufficient tangential force of the oil wiping rings is required to produce a radial contact pressure against the cylinder wall and thereby a good oil wiping effect. However, this results in a high surface pressure against the working surfaces of the lamellae, and therefore also a high friction power during engine operation. This friction power worsens the degree of effectiveness of the internal combustion engine and accordingly increases the fuel consumption. The design of the tangential force of the oil wiping rings is therefore always a compromise between minimal friction power and maximal oil wiping effect. All of the measures for reducing the friction power during engine operation, without reducing the tangential force, thereby facilitate the design of the oil wiping rings, i.e. improve the degree of effectiveness of the engine.
Accordingly, an attempt was made, for oil wiping rings of the type stated, aside from a special configuration of the spreading spring, to shape the working surfaces of the lamellae in such a manner that these meet the aforementioned requirements.
Asymmetrical working surfaces of oil wiping rings or piston rings are known from DE 38 33 322 A1, DE 43 00 531 C1, or DE 44 29 649 C2. Likewise, a piston ring is known from DE 33 05 385 C1, which is disposed in a ring groove of a piston, the ring groove side walls of which run preferably parallel, but at a slant to the piston axis, in order to guarantee a better seal. Ring groove side walls that are oriented at a slant and parallel to one another are also known from the Japanese utility model 57-73340. These previously known embodiments, however, relate to compression rings, whose requirements with regard to surface pressure are very low, while oil wiping rings demand great surface pressures.